The field of orthopedic medicine has grown tremendously in the past fifty years as surgical techniques, implants and instrumentation have developed and been improved. The medical companies have tended to focus their attention on the largest market areas so that some areas of the body, such as the spine, knees and hips, have received intense focus from the large medical companies. While the small bones are frequently subject to the need for re-constructive surgery for example, as a result of trauma, to counteract the effects of aging or to repair congenital deformities, this area has typically not received the same degree of attention from the medical companies as joint replacement, trauma and spinal areas. Consequently, the products available to the small bone surgeon often represent scaled down versions of products designed for the large long bone market which are not adequate for the fine bones and delicate procedures required of the small bone surgeon. Additionally, while there is a wide variety in the exact shape and mass of all bones, these variations become more problematic in providing orthopedic implants for small bone applications since there is less room on and about the bone for the surgeon to place and fix the construct. These bones are finer and have less surface area for placement of an implant, and less mass for the placement of screws and as a result, individual variations become more problematic for implants of stock design.
While some of the spinal companies have focused on hardware intended for use in the cervical and thoracic areas of the spine, some of the same problems exist in these areas as have been previously listed, thus the present invention is also useful in a slightly modified, and more robust form for use in the spine.
One problem that needs to be avoided in the delicate environment of the congested bone area, such as the metacarpals, the metatarsals, and the cervical region of the spine, is the interference of screws, with other screws, and with the function of ligaments and tendons. It may be desirable to design an orthopedic plate so that securing screws converge in order to cause compression or increase the pullout strength, it is difficult when a screw impinges on or conflicts with the desired placement of another screw. Some surgeons prefer bicortical fixation in which a screw is sized so that the distal end is secured in cortical bone giving the screw better purchase, however, other surgeons may prefer to avoid placing a screw so that it projects beyond the outer surface of the anchoring bone. These factors are complicated by the relative lack of soft tissue and the presence of ligaments and tendons in these small or congested bone areas. Consequently, the less forgiving biological environment in which the small bone or cervical surgeon works requires greater procedural precision and calls for specialized implants and tools.
The present invention is designed to meet the specific needs of the small bone surgeon to facilitate effective and repeatable procedures which provide for ease of use and a range of function for this specific area of specialization. The present invention could serve for the treatment of a broad range of indications including relatively straightforward fracture repair following trauma in an otherwise healthy individual where screws are used alone or with plates to maintain the integrity of the bones while they heal, as well as for more complex surgeries such as reconstruction to correct congenital or age related deformation. Reconstruction often includes arthrodesis or partial or total fusion which involves removal of a joint and the use of a mechanical-biological construct to keep the bones immobile while fusion occurs. Further small bone surgeons may be called upon to achieve soft-tissue balancing by readjusting the length of tendons and ligaments or to reshape the bone itself through removal or repositioning in a procedure known as an “ostetomy”. In an aging or diabetic population, these procedures may also involve dealing with the difficulties of poor quality bone and/or compromised soft tissue.
These surgeons typically include sub-specialists such as hand surgeons and feet and ankle and podiatric surgeons, but can also include general orthopedic surgeons who may be called upon to perform procedures on the small bones.
The present invention provides a plate with asymmetrical and bi-planar screw fixation and further designed to facilitate three dimensional contouring to provide for a variety of applications and to accommodate individual variation in bone shape. The plate is designed specifically for the small bone market, i.e. for use in bones distal to the elbow and knee, including, for example, the ulna, radius, tibia, fibula, as well as the metacarpals, carpals, metatarsals, tarsals, and phalanges, and in a further embodiment for the spine. The plate can be used in applications previously mentioned, for example those that require fixation to a single bone such as the stabilization of a fracture or the plate can be used across two or more bones so as to facilitate total or partial fusion. The plate is configured to bend laterally, longitudinally, and to wrap or spiral about its longitudinal axis so that it can be molded to an optimal shape for small bone procedures. The plate is designed to provide optimal stabilization of fractures and osteotomies by providing multi-planar fixation that allows for better pull-out and limited axial loading to the bone. The plate is further designed to accelerate fusion success by reducing or eliminating torsional or twisting stresses to the bone segments during the healing process. In addition, when desired, the plate can be shaped so as to apply a compressive, or even a tensile, force, for example, along the longitudinal axis of a bone.
The plate has a central trunk portion including one or more screw holes separated by a waist shaped linking portion along a longitudinal axis and a set of upper and lower arms including screw holes which are placed at a radially equal distance but which diverge asymmetrically from the longitudinal axis to avoid conflicts in the screw placement of the paired arm, specifically, so that the screws of a set of arms do not impinge on each other. The plate is radiused with a curvature corresponding generally to the curvature of a bony surface. The upper pair of arms, and the lower pair of arms continue this curvature and the through holes are placed so that the angle of the longitudinal axis of the screws converge in the direction of the distal end of the screw. The screw holes are placed with the longitudinal axis perpendicular a tangent to the top surface of the arm with the effect that the longitudinal axes of the screws converge in the direction of the distal end. This increases the pull-out strength of the screws. Further the screw holes are concavely rounded to allow for multi-axis orientation of the low profile, rounded screw in the hole, which can be oriented with a conical shape about the longitudinal axis of the screw hole having an angle of at least 20°, preferably at least 25°, and most preferably about 30°.
The screws do not in fact conflict since each of the arms in a pair form a different angle to the central trunk so that the longitudinal axis of the screws are offset from each other along the length of the plate. The pre-bent configuration of the plate is designed to increase operating room efficiency by facilitating commonly desirable shapes while maintaining the required strength and by permitting bending without deforming the screw holes. This results in making customization in anticipation or during surgery easier.
The screws useful with the plate of the present invention are self-starting, self-tapping screws including the option of partial or full cannulation. The screws include a cutting end having multiple flutes, and preferably 2 or 3 flutes about a conical recess. The screws further include a partial taper of the inner diameter in the proximal end over the first several thread turns, for example over 2-8, and preferably over 3-5 turns in order to increase the fatigue life of the screw as well as providing potential physiological advantages in use. The screw head is a rounded low profile head. The screws further include a torque driving recess that may be a hexagon, a torx shape, or a modification of a torx shape, i.e. a multilobe shape having from 3 to 12 lobes, and preferably having 4 to 8 rounded recesses or lobes. The recess can be of a constant size in the direction of the longitudinal axis, or can taper inward along the longitudinal axis of the screw toward the bottom of the recess.
The instruments for use with the system are well-balanced and ergonomically designed with sufficiently long handles to place the surgeon's hands outside of the line of radiation and designed to reduce fatigue in the operating room.
The plate system of the present invention is thus designed to fit a range of needs of the surgeon operating on the small bones (specifically including the small bones of the spine) to allow him or her to perfect a variety of techniques using a set of instruments and a customizable plate and screw construct.